You should see every interaction with someone who might be helpful to you and your business as a golden opportunity. Not making use of this opportunity in the best possible way is not only wasteful, it might be the make-or-brake moment of your company.
I made the mistake of not properly following up (or following up at all) in the past. The article points out why and how to follow up, but it’s all common sense really. There’s one more rule you should stick to (hat tip to swombat): always follow up on the same day.